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from .utils import _toposort, groupby
class AmbiguityWarning(Warning):
pass
def supercedes(a, b):
""" A is consistent and strictly more specific than B """
return len(a) == len(b) and all(map(issubclass, a, b))
def consistent(a, b):
""" It is possible for an argument list to satisfy both A and B """
return (len(a) == len(b) and
all(issubclass(aa, bb) or issubclass(bb, aa)
for aa, bb in zip(a, b)))
def ambiguous(a, b):
""" A is consistent with B but neither is strictly more specific """
return consistent(a, b) and not (supercedes(a, b) or supercedes(b, a))
def ambiguities(signatures):
""" All signature pairs such that A is ambiguous with B """
signatures = list(map(tuple, signatures))
return {(a, b) for a in signatures for b in signatures
if hash(a) < hash(b)
and ambiguous(a, b)
and not any(supercedes(c, a) and supercedes(c, b)
for c in signatures)}
def super_signature(signatures):
""" A signature that would break ambiguities """
n = len(signatures[0])
assert all(len(s) == n for s in signatures)
return [max([type.mro(sig[i]) for sig in signatures], key=len)[0]
for i in range(n)]
def edge(a, b, tie_breaker=hash):
""" A should be checked before B
Tie broken by tie_breaker, defaults to ``hash``
"""
if supercedes(a, b):
if supercedes(b, a):
return tie_breaker(a) > tie_breaker(b)
else:
return True
return False
def ordering(signatures):
""" A sane ordering of signatures to check, first to last
Topoological sort of edges as given by ``edge`` and ``supercedes``
"""
signatures = list(map(tuple, signatures))
edges = [(a, b) for a in signatures for b in signatures if edge(a, b)]
edges = groupby(lambda x: x[0], edges)
for s in signatures:
if s not in edges:
edges[s] = []
edges = {k: [b for a, b in v] for k, v in edges.items()}
return _toposort(edges)
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